Layout > Using Annotations > Tables > To Hide or Display Cell Borders
  
To Hide or Display Cell Borders
1. Select the entire table.
2. Perform one of the following operations:
To hide borders, click Annotate > Line Display > Blank and select one or more borders.
To display hidden borders, click Annotate > Line Display > Unblank and select one or more locations of the hidden borders.
To display all hidden borders, click Annotate > Line Display > Unblank All.